1. Field of the Invention
The present invention relates generally to the field of interior space illumination systems. More specifically, the present invention discloses a curved light shelf system mounted adjacent to a window to redirect incident sunlight into an interior space.
2. Statement of the Problem
It is a problem in the field of interior space illumination to provide a cost-effective mode of illumination that makes use of the incident sunlight without the need for complex systems or significant occupant intervention. For the purposes of this application, the term “daylighting” should be broadly construed to include any use of natural light from a clear sky (including daylight from both the solar disk and the sky dome) or overcast sky as an interior illuminant. Existing daylighting systems are either of limited effectiveness, limited applicability due to their architectural limitations, or require complex and expensive mechanical and electronic control mechanisms.
There is a need for systems that provide improved energy efficiency and environmental quality. One need is to reduce the consumption of electricity for lighting. One option for reducing electricity consumption for lighting is to use daylight to illuminate occupied building spaces. The key to the widespread use of daylighting systems is in providing a system that is both inexpensive and easily applied to both new and existing buildings. In addition to the savings attributed to reduced electricity consumption, daylighting systems typically also result in increased productivity by the occupants of the illuminated space, reduced health problems evidenced by the occupants of the illuminated space and pollution reduction. There appears to be a strong correlation between the quality of the luminous environment and the overall health and productivity of the occupants. These ancillary benefits can produce savings that dwarf the savings attributable to electricity consumption reduction, since studies indicate that, over the life of the building, an overwhelming percentage of the operating cost of commercial space is the salaries of the occupants. Thus, any improvement in the performance of the occupants of the building space results in a significant economic benefit.
One such existing daylighting system is the traditional light shelf, which receives daylight through a window and redirects it onto the interior ceiling plane, thereby creating a useful source of interior illumination. The basic light shelf concept typically comprises a wide flat elongated interior light shelf located adjacent to a window that protrudes into a room from the exterior wall of a building. The incident sunlight is reflected by the light shelves onto the ceiling of the occupied space by a diffuse or specular horizontal or slightly-sloped upper surface of the light shelf. However, an interior light shelf typically protrudes a significant distance into the occupied space and is problematic from architectural, mechanical and aesthetic standpoints in many room applications.
FIG. 3 is a side cross-sectional view of a typical prior-art light shelf daylighting system. This daylighting system includes at least one light shelf 30 located in the interior space 28 of a building adjacent to a window 20. Each light shelf 30 is oriented in a substantially horizontal plane with its outer edge adjacent to the window 20. If multiple light shelves are employed, they are typically stacked in a vertical arrangement similar to conventional blinds. Optionally, light shelves can also be located on the exterior 26 of the building adjacent to the window 20.
The basic light shelf concept typically includes a wide flat elongated interior light shelf 30 located adjacent to a window that protrudes into the room from the exterior wall of a building to receive incident sunlight 10, as illustrated in FIGS. 3 and 6. The incident sunlight 10 is reflected by the light shelf 30 onto the ceiling 24 of the interior space 28 by the top surface of the light shelf 30. In the embodiment depicted in FIGS. 3 and 6, the top surface of the light shelf 20 is located a predetermined distance below the ceiling 24, and divides the window 20 into a view area 21 below the light shelf 30, and a daylighting area 22 above the light shelf 30. The view area 21 can be equipped with a conventional shade control to controllably regulate the intensity of the incident daylight that is transmitted to the interior space 28 as well as to enable the occupants of the interior space 28 to control the visibility of the interior space 28 from outside the building. No means is typically provided to block the incident daylight through the daylighting area 22, although a shade element may be provided for blackout purposes, or to block light from low angles of elevation that may otherwise bypass the light shelf and cause unwanted glare.
3. Prior Art
The prior art in the field of light shelves and other devices for reflecting sunlight into an interior space includes the following:
U.S. Pat. No. 284,963 (Hyatt) discloses of a system of flat louver-type blades mounted in an arrangement similar to that of a hinged louvered register. This system is designed to pass natural daylight into an interior room through reflectance from the fiat, louvered blades. The system is designed to pivot on a hinge and be operated by a rope-and-pulley system to allow the building occupant to adjust the daylight. One shortcoming associated with this system is that it relies on the operator for continual adjustments. The system also relies on it being placed on a rooftop, more in the fashion of a skylight rather than in a wall system. This renders the invention less useful on multiple-level buildings since only the top floor can be used for daylighting.
U.S. Pat. No. 1,567,984 (Reid) discloses a system having a flat reflector plate with a corrugated surface hinged about the interior of a window system. This invention employs many traits of a traditional light shelf in that a light collection area reflects light toward the ceiling of a room. The shortcoming associated with this system is that it tends to direct light in concentrated areas on the ceiling called “hot spots”. The irregular surface that this system utilizes would do little to scatter light deeper into the interior space.
U.S. Pat. No. 1,747,928 (Chesney) discloses a system of curved reflector plates mounted to both the inside and outside of the window. The outermost reflector plates are concave to reflect and concentrate light. The concave members predominately face each other to concentrate and direct the light inward toward a third reflector plate. The third reflector plate is convex and scatters the light toward the floor. One shortcoming is that exterior-mounted reflectors are subject to the elements such as wind, snow, rain, and pollution. When dirt or snow collects on the exterior reflector plates, they become ineffective at collecting the daylight. A second shortcoming is that it requires a substantial vertical distance of window to operate correctly. This inhibits the view portion of most windows, therefore making less of the outdoors visible from the interior of the building, and making occupants feel more closed in than if there were no apparatus installed. A third shortcoming is that of concentrating light. Concentrated light can cause intense heat and with that an increased risk of fire. Finally, the light diffused by the third convex reflector is directed toward the floor and the building occupants, which creates undesirable glare. Intense sun glare can have a negative impact on building occupants.
Japan Patent No. 58-199314 (Tomofuji) discloses a small-sized concave light condensing device. This is opposite of a daylighting device that produces diffuse light. Instead, the Tomofuji device collects and concentrates light into one area.
U.S. Pat. No. 4,630,892 (Howard) discloses a system of three flat surfaces, with two mounted on the exterior, and one mounted on the interior to reflect and direct light inside a building. This can cause hot spots and also requires constant building occupant adjustment for changing sun angles.
U.S. Pat. No. 4,634,222 (Critten) discloses a natural-light illumination enhancement assembly having a series of louvered reflectors that direct incoming light downward onto the floor for illumination. Here again, this creates glare downward on building occupants.
German Patent No. 3831318 (Hesse) depicts a system of flat prismatic-shaped surfaces that direct light into a space from the exterior side of a building. This is an encased system that is placed in the ground to direct light into basements. Debris, snow, or dirt can gather on the intake side of the system since it is exposed to the elements, and inhibit the effectiveness of the system. The system also would direct light in hot spots.
German Patent No. 020296 (Jurastrasse) depicts of a system of a plurality of concave elements similar to a Venetian blind. The shortcomings associated with this system include keeping the surface behind the device clean. Also this system uses a substantial amount of vertical space thereby allowing more heat gain inside the building. Also this system blocks the view of the occupants to the out-of-doors.
U.S. Pat. No. 5,293,305 (Koster) discloses a system of vertical concave elements within a window system to direct light upward toward the ceiling. This system appears to be relatively complicated to implement and would offer an obscured view through the window. This system also uses a substantial amount of vertical space to implement.
U.S. Pat. No. 5,802,784 (Federmann) discloses a system of vertical concave elements within a window system to direct light upward toward the ceiling. This system appears to be relatively complicated to implement and would offer an obscured view thru the window. This system also uses a substantial amount of vertical space to implement.
U.S. Pat. No. 5,285,315 (Stiles) discloses a system that uses light-reflective elements sandwiched between two panes of glass to redirect sunlight into the interior space of a building. The reflective elements comprise both stationary and movable elements that function to redirect the incident sunlight to the back walls of the room, above eye level without striking the ceiling. A shortcoming associated with this light reflecting system is that it is complicated to implement and produces illumination of variable quality. The existing glazing must also be replaced to implement this system.
U.S. Pat. No. 4,557,565 (Ruck et al.) discloses a system of refractive structures that are used to collect and redirect light into a building. The refractive structures comprise a planar solid transparent light deflecting panel or plate that is formed of a plurality of parallel triangular ribs located on one face. With the panel in its vertical orientation and placed over a window opening, the panel reflects sunlight into the building interior. The panels are designed to require seasonal adjustments to compensate for the seasonal variations in the angle and nature of the incident sunlight. The refractive panels are complicated to implement and require periodic adjustment by the occupant to compensate for changes in the incident sunlight.
U.S. Pat. No. 5,293,305 (Koster) discloses a light guidance system that illuminates the interior of a building by using a light deflection device equipped with a light source. The light guidance system is mounted in a window and both reflects sunlight coming from outside of the building as well as electric light coming from the light source. The light guidance system comprises several light reflective elements that are disposed parallel to one another and spaced apart from one another such that light from outside the building is reflected by the top surface of the light reflective elements and light from an internal light source is reflected by the bottom surface of the light reflective elements into the room. The light reflective elements function both to shade the interior from direct sunlight while also redirecting both the incident sunlight and the light from the light source into the room to provide indirect lighting. A problem with this light guidance system is that it relies on the close spatial-optical relationship between the electric lighting located at the window and the incident sunlight through the window. Another problem with this light guidance system is that it blocks the view through the window and relies on the placement of a source of electric light at the window. Thus, it is expensive to implement and requires expensive adaptation of existing installations to accommodate the light source.
U.S. Pat. No. 4,883,340 (Dominguez) discloses a solar lighting apparatus that is mounted on the roof of a building to provide illumination of the interior of the building. The solar lighting apparatus comprises a reflector assembly that is rotatable about a vertical axis for tracking the daily movements of the sun. The reflector panel has multiple panels that are mounted on a frame over a skylight opening and the frame is rotated by the operation of solar tracking electronics. However, the solar lighting apparatus is effective only for the room area located on the top floor of a multiple story building. In addition, it relies on electronics and mechanical tracking apparatus to collect and redirect the incident sunlight.
U.S. Pat. No. 6,239,910 (Digert) discloses a mini-blind system similar to that of a window treatment or blind. This system is unique due primarily to the curved nature of the individual blades. This type of optical device, while more efficiently scattering the light than a traditional flat light shelves, creates problems similar to that of traditional window treatments such as the need to continually clean the interior surface of the window directly behind the apparatus. Maintenance personnel can easily damage this type of system making it impractical in most commercial settings. Once a single blade of this system is bent it can direct light inadvertently into buildings occupants' path of vision, creating discomfort. Also, this type of system is mounted vertically. This requires significant square footage of window surface area to allow ample sunlight to penetrate. It is known that letting natural daylight penetrate the building has the inherent drawback of solar heat gain that can increase the buildings cooling system loads substantially in summer months. Often the increased costs of operating such cooling systems can outweigh the benefit gained in electricity savings of interior daylight illumination.
U.S. Pat. No. 6,389,216 and U.S. Pat. No. 6,490,403 (Bartenbach et al.) disclose a system having a rolled sheet that is toothed with flat surfaces to guide the light in a particular direction. This system is meant to be installed in conjunction with a daylighting device such as a light shelf to redirect daylight that already has been cast to the ceiling.
U.S. Pat. No. 6,480,336 (Digert et al.) discloses a system of concave-curved slats that are vertically stacked, similar to Venetian blinds or that shown in U.S. Pat. No. 6,239,910. Due to its nature, the shortcomings are very similar in those of both devices. One other shortcoming is that this is a static device that cannot be easily removed to access the surface directly behind it for regular cleaning.
U.S. Pat. No. 6,580,559 (Doll et al.) discloses a system having a vertically-arranged plurality of flat members placed within a window system for directing light. This system has shortcomings similar to that of U.S. Pat. Nos. 6,239,910 and 6,480,336, being as it is predominately vertical and uses a large amount of viewable window space to implement.
U.S. Pat. No. 6,714,352 (Rogers et al.) discloses a system having a vertically-arranged plurality of concave-shaped sections with flat bottom surfaces. This system has shortcoming similar to those of U.S. Pat. Nos. 6,239,910, 6,480,336, and 6,580,559 since it is arranged in a similar vertical fashion.
Thus, the field of interior space illumination systems appears to be devoid of an inexpensive, practical, effective, and simple-to-use daylighting system that can be easily implemented in both existing building applications as well as in new building construction. The problem with most existing systems is that they either take up too much vertical window space that could be otherwise used for view, they are difficult to maintain, require frequent occupant intervention, or cast light in concentrated patterns creating hot spots.
Architectural Moldings. The prior art in the fields of moldings, architectural trim and picture frames includes a family of decorative cross-sectional profiles commonly referred to as cyma-reversa curves. This profile is also sometimes referred to as an ogee curve. For the purposes of this disclosure, these terms are used synonymously. A cyma-reversa profile has a region with a convex surface followed by a region with a concave surface. In other words, an initial region a cyma-reversa curve bulges outward and is followed by a second region that bows inward. These regions can flow together in a smooth, continuous manner, somewhat similar to a relaxed S-shape. Alternatively, these regions can be clearly demarcated and separated from one another. Although cyma-reversa curves have been employed in moldings, picture frames and architectural details for their aesthetic appeal, they are not believed to have been applied to the field of reflectors or light shelves in particular.
Solution to the Problem. The above-described problems are solved and a technical advance achieved in the field by the present curved light shelf daylighting system having a cyma-reversa profile. In particular, the present curved light shelf is a passive, static optical device that can be mounted horizontally adjacent to a window of a building. The curved light shelf receives daylight transmitted through the window and efficiently redirects it onto the ceiling of an interior space in a diffuse manner, double washing the ceiling with a relatively even amount of illumination, thereby creating a useful source of interior illumination that is free of hot spots and is cast deeper into the room than the conventional light shelves.
The curved light shelf comprises a single predominately horizontal shelf, that is optically shaped via a cyma-reversa top surface to allow light to be efficiently collected and accurately directed onto the ceiling plane of a room, while at the same time shading the occupants of the room from direct sunlight penetration through the shelf. The curved light shelf is narrow and can be implemented in the normally unused upper foot, or so, of most interior spaces.
The window area may or may not be partitioned by the light shelf into a view section and a daylighting area. The occupants' views out of the building remain relatively unobstructed through the view area of the glazing to a height of approximately seven feet, or greater, above the floor. Traditional window treatments, such as exterior shading devices, or interior blinds can be used for this portion of the glazing for shading, privacy, and blackout control. The sunlight incident on the daylighting area of the glazing is collected by the curved light shelf and redirected onto the ceiling plane of the room in a glare-free manner.
The curved light shelf system produces effective daylighting for typical ambient light levels for the perimeter zones of a building, and can operate for room depths in excess of fifty feet. The optical geometry of the light shelf and the associated reflective surface characteristics diffuse the collected sunlight more evenly over a larger area of the ceiling plane of the room. The resultant indirect lighting is striation free and substantially uniform in luminance. The use of daylight preserves the visual and psychological connection between the occupants and the outdoors due to the subtle color and luminance changes which occur throughout the day. Visual comfort is enhanced by evenly diffusing the daylight across the ceiling plane of the room from the perimeter wall to the interior extent of the illumination.